[llvm-dev] linker adaptability ... (original) (raw)

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Tue May 19 11:03:24 PDT 2020

Hi Kris,

Dave is right: You'll want to check out ORC and JITLink. As a starting point I'd recommend taking a look at this example that uses a JITLink plugin to render the JIT-linker's graph data structure: https://github.com/llvm/llvm-project/blob/master/llvm/examples/OrcV2Examples/LLJITWithObjectLinkingLayerPlugin/LLJITWithObjectLinkingLayerPlugin.cpp

JITLink is currently only available on Darwin, but someone just posted a review for an under-development ELF version: I expect that to land in-tree this week and quickly develop enough relocation support to handle basic use cases.

Regards, Lang.

On Mon, May 18, 2020 at 7:45 PM David Blaikie <dblaikie at gmail.com> wrote:

Sounds like you're probably after ORC https://llvm.org/docs/ORCv2.html - a JIT infrastructure, which as you've described, models object files and executable code in-memory as closely as possible to the on-disk format, and supports things like replaceable code.

On Mon, May 18, 2020 at 6:25 PM kris via llvm-dev <llvm-dev at lists.llvm.org> wrote:

hello folks,

I'm working to add runtime updating of code to the OCaml compiler which in its bytecode guise presents no barrier because there is only one linker and it is written in that language and full control is available. With native code on the other hand, there is reliance on the system linker and I got completely lost examining the GNU ld/dl library source code. The prospect of understanding and modifying all possible linkers is daunting to say the least. It's finally dawned on me that LLVM might have some of what I need already. Would you be kind enough to examine the following wish-list and comment on it's current viability with respect to the LLD project? 1. to load and link a set of object/archive files into an in-memory executable. 2. to track the memory allocations attributable to each contributing object processed with a view to releasing them. 3. to maintain the symtable in-memory with a view to updating symbols and re-patching the in-memory executable. 4. to reload an object file/archive member (or a new one) and process it in accordance with 3. No doubt LLD is not geared to any of this directly, but does the library provide any support? thanks in advance....

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